Ir-based Schottky and Ohmic contacts on n-GaN

IrAu Schottky contacts and TiAlIrAu ohmic contacts on n-type GaN were investigated as a function of annealing temperature and compared to their more common Ni-based counterparts. The IrAu ohmic contacts on n-type GaN with n≈ 1017 cm-3 exhibited barrier heights of 0.55 eV after annealing at 700°C and displayed less intermixing of the contact metals compared to NiAu. A minimum specific contact resistance of 1.6× 10-6 cm-2 was obtained for the ohmic contacts on n-type GaN with n≈ 1018 cm-3 after annealing at 900°C. The measurement temperature dependence of contact resistance was similar for both TiAlIrAu and TiAlNiAu, suggesting the same transport mechanism was present in both types of contacts. The Ir-based ohmic contacts displayed superior thermal aging characteristics at 350°C. Auger electron spectroscopy showed that Ir is superior to Ni as a diffusion barrier at these moderate temperatures.